The proposed investigation seeks to compare behavioral and psychoendocrine response of singly-housed adult male macaques of two species (Macaca fascicularis and M. silenus, to varying social stimuli for the purposes of systematic resocialization, group formation, and group living. The resocialization procedure is progressive, in that the subjects will be exposed to social stimuli in stages in which the stimuli become increasingly complex. The investigation will consist of four phases or conditions which include 1) pre-exposure (baseline) in which behavioral data are collected from the subjects housed singly; 2) mirror exposure, in which responses to the comparatively "inanimate" stimulus of their reflection are measured; 3) pairwise social introductions of conspecifics; and 4) group formation, in which responses to simultaneous social introduction of conspecific subjects is measured. Psychoendocrine response (urinary cortisol and testosterone levels) will be measured before and during each of the social conditions. The study is designed to test the efficacy of systematic resocialization procedures for animals with restricted social experience, to compare psychoendocrinological responses to varying social stimuli between species, and to document possible differences in behavior-hormonal relationships for each species. The investigation has implications for the husbandry and management of the subject species and the well-being of other captive macaques, and for the understanding of psychoendocrine differences in responsivity between related primate species.